Mycoplasma bovis (M. bovis) is considered to be one of the more pathogenic species of Mycoplasma and causes significant economic losses worldwide. Mycoplamsas cause severe clinical signs in cattle of all ages. M. bovis is the most frequent Mycoplasma pathogen found to cause pneumonia, mastitis, and arthritis in cattle and its etiological role has also been associated with otitis, keratoconjuctivitis, synovitis, and reproductive disorders in cows and bulls. In general, Mycoplasmas are difficult to treat since they lack a cell wall or membrane, which tends to make them resistant to several classes of commonly used broad-spectrum antibiotic treatments. Mycoplasmas differ from viruses in that Mycoplasmas are larger than most viruses and damage tissue cells by attaching to the surface of cells and destroying them, rather than by entering the cells. Animals infected with M. bovis have depressed immune responses and can exhibit signs of M. bovis infection such as fever, depression, anorexia, labored breathing, nasal and ocular discharge, coughing, sneezing, gasping, grunting, lameness and swollen joints, mastitis, middle ear infections, abortions, recumbence and death. The organism persists in unsanitary, warm, moist environments. Mycoplasmas can survive in milk, and even seem to thrive in the presence of large numbers of leukocytes, which are produced in response to the infection.
There are several references available in the art disclosing M. bovis vaccines. U.S. Pat. No. 6,548,069 discloses a vaccine composition that incorporates a whole cell inactivated bacterin containing at least two killed M. bovis strains. Other references available disclose passaging an M. bovis strain less than 10 times to prepare an inactivated vaccine, but do not describe attenuation of an infectious or pathogenic M. bovis strain through serial passaging or any such attenuated live M. bovis strain as the essence of avirulent live culture vaccine.
The prior art is deficient in that killed M. bovis is not as effective or efficient in lessening the severity of clinical symptoms associated with a Mycoplasma bovis infection. Even passage at a low level does not produce a Mycoplasma vaccine with high efficacy such that clinical symptoms are greatly reduced. The few low passage, inactivated, M. bovis vaccines that are available do not show a large reduction in the severity of clinical symptoms. Additionally, the '069 patent strongly teaches away from the idea of a high passage, attenuated strain of M. bovis being used in an immunogenic or vaccine composition by teaching:                “Because a Mycoplasma isolate may rapidly alter its antigens in culture, high passage strains of greater than about 50 passages may lose infectivity and elicit a poorer immune response when used in a bacterin of the present invention. Therefore, it is preferable to employ freshly isolated strains or cultured strains that are still virulent; that is, strains that have retained the ability to be infectious in the host animal. While no critical number of generations is known to exist, the present invention preferably starts with a Mycoplasma strain which has been passed no more than about ten, and preferably only about five or less times before mass scale production. By using strains with fewer generations in culture, it is believed that the antigens retain their natural state and thus will elicit a protective immune response against the infectious microorganism.”        
Accordingly, what is needed in the art is an immunogenic composition effective for eliciting an immunological response against M. bovis. What is further needed is an immunogenic composition effective for lessening the severity of or reducing the incidence of signs of M. bovis infection. What is still further needed is a vaccine effective for reducing or eliminating the incidence of signs of M. bovis infection. What is still further needed is an immunological composition effective for lessening the severity of or reducing the incidence of signs of M. bovis infection that can be safely administered to an animal in need thereof. What is still further needed is an immunological composition as described above that induces cross-protection and provokes an immune response against different M. bovis strains and isolates than those strains or isolates used in the composition. What is still further needed is a safe and effective immunological composition that is suitable as either a one dose or two dose or multi-dose (initial dose followed by booster(s)) immunization regimen, an immunological composition suitable and convenient for administration by several routes, and an immunological composition that is compatible with other immunogens and immunological compositions for preparation of combination vaccines. Finally, what is needed is an immunological composition as described above that provides rapid onset of protection and long-lasting protection to an animal in need thereof.